This invention relates to an electric quick-break switch of a type including supplemental means for forcing the normally closed contacts of the switch to open, in the event they otherwise fail to open upon switch actuation, as for example due to the slight welding together of the contacts.
Quick-break switches are mainly utilized in travel limiting devices, which are largely employed in the fields of sequential operation controls, control of the travel limits of machine tool slides, and the like.
Several national and international standards require that certain systems, such as travel limiting devices, be equipped with a switch devised to ensure that the normally closed contacts are opened even in the event of failures in any part of the switch.
A known technique of ensuring a positive opening of the contacts is that of connecting in series to the normally closed contacts, another pair of contacts, also normally closed, which are opened by an override movement of the quick-break switch actuating members. This approach has the disadvantage of being bulky and expensive.
A further technique, for ensuring a positive opening of the contacts, provides a mechanical means effective to urge the movable portion of the contact pair to open whenever its correct opening by the actuating members fails to occur. This is accomplished in one of two ways. One solution provides a lever of any sort which is supported on the bottom of the switch body and is pushed to one end by a member connected to the switch actuating mechanism as an extension of an actuating button or rod. Such a mechanism, while effective, requires that the switch be arranged in a vertically upright position with the actuating button pointing upwards. The other solution provides two or more levers journaled to the sidewalls of the switch body and having one end acted upon by a cam surface connected to the actuating button, causing the other end to become adapted to strike the movable portion of the contacts, which is accomplished through an additional or override movement of the button. Successful operation is still related to the switch body position. When the switch is positioned with its actuating button pointing downwards, the actuating levers, if not perfectly balanced, may pivot by gravity to rest against the movable portion of the contacts, thus impairing the opening operation accuracy and possibly hindering the free movement of the actuating button itself.